Petrographic, geochemical and geochronological characterisation of Batavia Knoll Dredge samples, Perth Abyssal Plain: implications for linkage with Gondwana

This study heralds the discovery of a submarine micro-continent called Batavia Knoll, confirming its previously unknown continental crust affinity. The Knoll is submerged under approximately 2km of water on the Perth Abyssal Plain, some 1600km west of the Western Australian coast. Detailed petrographic, geochemical and geochronological analysis of seven representative dredge samples from Batavia Knoll has enabled the characterisation of these rocks, and thus of the Knoll. It is comprised predominantly of granites, granite gneisses, intermediate gneisses, schists and sandstones. The majority of the analysed granitoids (n=6) record emplacement and orogenesis from the latest Neo-Proterozoic to Cambrian. These rocks subsequently enjoyed tectonothermal activity soon after emplacement, marked by zircon disturbance and metamorphic/deformation textures. Older basement rocks were not sampled, unless the zircon poor intermediate gneisses are significantly older than the granitoids. The dredged sandstone rocks were not examined in this study, but likely represent rift-related sedimentation during Gondwana dispersal at ca.132 Ma. These sandstones will be examined at the University of Sydney. The presence of orogenic activity associated with Gondwana amalgamation between 600-500 Ma combined with current plate tectonic reconstructions allows for the correlation of Batavia Knoll with the Kuunga Orogeny.